This invention relates to chucks for holding work pieces in lathes or like work piece rotating machines and particularly to means for rigidly holding the jaws against movement.
To carry out the present day precision in lathe work it is essential that the jaw faces which bear against the work accurately define a circle which is in absolute axial alignment with the axis of the work piece. This can be achieved by individually adjusting the jaws radially back and forth until the work is positively positioned in its intended location, but this is a very time consuming and tedious task. The working time which is lost in such a procedure is totally inconsistent with high productivity.
Various short cuts have been devised to shorten the setup time to accurately position the work piece and one of these ways is to provide the jaws with so-called soft material which can relatively easily be machined. This soft material makes it possible to rotate the chuck on the lathe in a normal manner and machine the soft material to absolutely accurate concentricity to receive the work. However, even this has its limitations as the slight slack which exists between the operating parts of the chuck mechanism results in a more or less malpositioning of the jaws.
The present invention provides means for firmly holding the jaws in fixed positions relative to the chuck body so that its faces which are to receive and grip the work can be machined to the size which will accommodate the workpiece. Then when the workpiece is placed between the jaws and the jaws are tightened against the work, the workpiece is accurately positioned axially and it can be machined with absolute precision.
The time required to bring the jaws to this accurate position is minute compared to the time required to individually adjust the jaws. Moreover, the use of the jaw locking means of this invention requires significantly less time and produces greater accuracy of positioning the jaw faces than the other means which have been devised.
The means of this invention is an improvement on the arrangement disclosed in U.S. Pat. No. 3,679,221 which issued to A. J. Behrens on July 25, 1972. This patent shows an eccentric wheel 84 which is mounted on a transverse shaft 82 so that when the wheel is turned and wedged against the face of the chuck body the effect will be to wedge the jaw itself against motion. The structure of the patent has some utility but as the eccentric wheel has merely a camming action to hold the jaw in place, it is not fully satisfactory. The structure provided by the present invention is simple and inexpensive and serves to rigidly hold the jaws in position on the chuck body. The invention can be applied to the jaws of the aforesaid patent to take the place of the wedge wheel and in order to show a representative application of the invention this description and drawings illustrate this use. This makes it unnecessary to illustrate the internal mechanisms of the chuck since the patent can be referred to for this disclosure. For this reason the structure and wording of the patent are hereby incorporated herein by this reference.
In the Applicant's prior application Ser. No. 398,106, filed July 14, 1982 there is disclosed one arrangement for rigidly holding the jaws in position on the chuck body, this arrangement comprising a U-block mounted for movement in a transverse passageway in the soft jaw. In application Ser. No. 612,257, filed May 21, 1984 the applicant has shown another means for rigidly holding the jaws in position on the chuck body, this means comprising a straight block contained in a transverse passageway in the soft jaw and having a pair of untarely mounted leg members in the extended ends thereof for contacting the chuck face. In accordance with the present invention there is provided another means for rigidly holding the jaws in position on the chuck body.
Briefly stated, the present invention comprises an improvement in a lathe chuck having a master jaw guided for sliding movement relative to the chuck body in ways in the chuck body, and a soft jaw mounted on and secured to the master jaw for conjoint movement therewith as a unit, the master jaw and the soft jaw unit being mounted for movement across the face of the lathe chuck as the master jaw slides in the chuck ways, the chuck ways and the master jaw having opposed surface portions limiting movement of the master jaw toward the chuck face, the improvement comprising a slot formed in the bottom of the soft jaw extending transversely therethrough and means for frictionally locking the master jaw and the soft jaw unit in a fixed position relative to the chuck body including a block mounted in the transverse slot and having portions extending laterally from the sidewalls of the soft jaw and leg members extending from said extended portions of the block towards the chuck face for frictionally engaging the same at the ends of the leg members and actuating means for causing the ends of the leg members to come into frictional engagement with the chuck face and the soft jaw to move away from the chuck face to cause opposed surface portions of the master jaw and the ways to be frictionally engaged so that the master jaw and the soft unit is frictionally locked in a fixed position relative to the chuck body.